Purpose: Using the recrystallization method to determine the solubility of a variety of solutes added to a variety of solvents and observing crystal formation conducting a series of tests. Theory: Recrystallization is a method for purifying solid organic compounds. The goal is to remove impurities from a solid to result in crystal lattice growth. An impure organic solid will not demonstrate well-defined crystals due to impurities preventing crystalline structures to form. Pure organic substances are held together primarily by London forces. These forces are fairly week and demonstrate a wide temperature range to melt most organic solids. During recrystallization, the material used is dissolved to be purified, or ‘the solute’, in hot solvent to yield a solution. Solubility demonstrates soluble in hot solvent, while insoluble in cold solvent. Saturation level occurs when the solvent becomes saturated with the solute as it cools. Recrystallization occurs when the solution becomes saturation with solute. In exclusion, the solvent doesn’t become saturated with impurities. The impurities stay in the solution and are excluded from the crystal structure. Crystals grow from a point of nucleation, which can be a seed of crystal or a speck of dust. The 7 steps of recrystallizing: 1) Choosing the solvent or solvent pairs; 2) Dissolving the solute; 3) Decolorizing the solution; 4) Filtering suspended solids; 5) Recrystallizing the solute; 6) Collecting and washing the crystals; 7) Drying the crystals. Reactions: N/A Table of Reagents: Compound: Benzoic Acid Structure MW Amount to be used 122.12 140 mg Physical constants and cautions Harmful if swallowed, may cause skin irritation Anthracene 178.23 40 mg Harmful if exposed topically and systemically; handle as a carcinogen and mutagen. May cause skin irritation Resorcinol 110.1 40 mg Alanine 89.09 40 mg May be harmful if digested Toluene 92.14 4 mL Water 18.01 As needed Harmful if digested, skin and eye irritant, flammable liquid and vapor Nontoxic Cyclohexane 84.16 4 mL Ethanol 46.07 4 mL Phthalic Acid 166.14 100 mg Flammable liquid and vapor, harmful if swallowed or inhaled, skin irritant, toxic to aquatic life Flammable liquid and vapor Skin and eye irritant, may cause respiratory irritation Methanol 32.04 20 drops Flammable liquid and vapor, harmful if swallowed, skin and respiratory irritant Pelletized Norit 12.01 A few pellets May cause respiratory irritation, suspected of carcinogenicity Procedure: I. Solubility Test 1. Add 10 mg of benzoic acid to 4 test tubes; label each tube: Toluene, Water, Cyclohexane, Ethanol. 2. Add each solvent it int’s respective tube. 3. Flick each test tube for 1-2 minutes; observe solubility. 4. If soluble: record data and add drops of water. i. If cloudy, heat mixture and add additional drops of solvent solution is clear 5. If not soluble: heat for 2-3 minutes. i. If soluble: record and cool solution to observe crystal formation ii. If not soluble: record data 6. Repeat steps 1-5 for solutes: Anthracene, Resorcinol and Alanine. 7. Record observation as ‘soluble’ and ‘insoluble’. II. Phthalic Acid Recrystallization 1. Add 100 mg of Phthalic acid in a reaction tube with 10 drops of water. 2. Gently heat solution with boiling stick. 3. Add 12 drops of water until solid is dissolves. 4. Use an ice bath to cool the solution and observe crystal formation. 5. Weigh filter and place in Hirsch funnel to filter out crystals. 6. Place in lab drawer for next lab. 7. Measure the weight and determine the percent recovery. III. Decolorization 1. Add a few pelletized Norite to a colored solution. 2. Boil. 3. Observe the reaction and record data. IV. Benzoic Acid Recrystallization 1. Observe the reaction of two test tubes; label each test tube appropriately. 2. Test Tube #1: i. Add 50 mg benzoic acid and 15 drops of methanol in test tube. ii. Heat to a boil. iii. Add 10 drops of water to dissolve benzoic acid. iv. Place test tube in an ice bath and observe crystal formation. v. Record observation. 3. Test Tube #2: i. Add 50 mg benzoic acid and 15 drops of methanol in test tube. ii. Heat to a boil. iii. Add 8 drops of methanol to dissolve benzoic acid. iv. Remove from heat and add cold DI water until solution is cloudy. v. Place in ice bath and observe crystal formation. vi. Record observation. Results: I. Solubility Test Cold Solute/ Solvent Benzoic Acid Anthracene Resorcinol Alanine II.   Cold S INS INS INS Hot Water --S S INS INS INS S S Cold Hot Cyclohexane S INS S INS INS S --- INS INS --- INS INS Phthalic Acid Recrystallization Filter Filter & Crystal Crystal  Hot Toluene 0.035 g 0.174 g 0.139 g Water added: 22 drops o 20 drops = 1 mL  22 drops = 1.1 mL (or 1.1 g) Phthalic acid added: 100 mg (or 0.1 g) Percent recovery = (pure / impure) x 100 Percent recovery = (0.139 g / 1.2 g) x 100 = 11.6% Cold Hot Ethanol S INS S INS --S --INS III. Decolorization (Solution after boiling pelletized norit.) IV. Benzoic Acid Recrystallization Test Tube #1: Test Tube #2: Needle Crystal Structure Prism Crystal Structure Discussion: In regard to solubility, Benzoic Acid demonstrates solubility in a cool toluene solvent, hot water solvent, hot cyclohexane solvent, and cool ethanol solvent; while insoluble in cool water and cool cyclohexane. Anthracene demonstrates solubility in hot toluene solvent, hot cyclohexane solvent, and hot ethanol solvent; while insoluble in all 4 cool solvents. Resorcinol demonstrates solubility in hot toluene solvent, cool water solvent, and cool ethanol solvent; while insoluble in cool toluene and cool cyclohexane solvent. Alanine demonstrates solubility in cool water solvent while insoluble in the remaining 3 cool and hot solvents. The ideal solvent will dissolve the solute when the solution is hot but not cold; either the impurities will not dissolve or dissolves very well. The solubility tests demonstrate the polarity of the solvents and their ability to dissolve with the solutes. In regard to the phthalic acid recrystallization test, the percent recovery demonstrates a significant amount of phthalic acid was lost after the completion of the chemical reaction. There could be several reasons that may have caused this: incorrect weighing and/or recording of the filter and the filter with crystal, incorrect use of the Hirsch funnel to filter crystals, incorrect recording of drops of water added, and incorrect heating of the solution. During the decolorizing test, when the activated charcoal was added there was no change to the color of the solution. Once the solution was brought to a boil, the charcoal demonstrated its removal of the color from the solution, ‘exorbtion’, and the charcoal was observed to ‘climb’ the test tube walls during boiling. The solution was not filtered, simply observed. No complications occurred during this test; however improper documentation led to the uncertainty of the colored solution used. Testing benzoic acid recrystallization, the test tube (#1) that included water in the benzoic acid, methanol solution demonstrated crystals in needle structures in a cloudy solution, while the test tube (#2) with additional methanol drops developed more prism like crystal structure. Due to improper documentation, the percent recovery in water and in solvent pair was unable to be determined. Although the steps of recrystallization were not completed as a single procedure but rather broken down in several parts, the results provide a more in-depth understanding on how each step of recrystallization occurs. One can assume, when completing the steps throughout, would experience similar results. Precautions to keep in mind, with impure substances slower cooling ensures maximum purity and weaker intermolecular forces result in higher free energy. If cooled rapidly, impurity can become entomb within growing crystal, causing a discrepancy in results. Also, it is important to always wash crystals in cool water; never hot. Conclusion: This lab demonstrates the steps of recrystallization and determining percent recovery of crystal formation for phthalic acid and benzoic acid. Recrystallization is an efficient method of purification and understanding London forces. Although some complication occurred during the experiment, the data yields favorable results with regards to the theories tested. Post Lab Questions: 3) Why should activated carbon be used during a recrystallization? Activated carbon is also a decolorizing carbon, used to remove the colored impurities from a sample. Activated carbon has a high surface area that allows the absorption of colored impurities. 5) Under which circumstances is it wise to use a mixture of solvents to carry out a recrystallization? When you want to separate the impurities in a solution. The mixture with an added solvent which the impurity is soluble in but immiscible with the other solvent. It allows for an easier separation of the impurity from the product. 6) Why is gravity filtration rather than suction filtration used to remove suspended impurities and charcoal from a hot solution? Suction filtration will cause a hot solution to boil then vaporize, causing a suction of vapor rather the actual liquid being filtered. 9) Why is the final product from the recrystallization process isolated by vacuum filtration rather than gravity filtration. Due to crystals needing to stay cold to remain pure and solid, gravity filtration may add heat to the solvent causing the crystals to dissolve. Vacuum filtration allows the removal of the solvent while still maintaining a cold temperature. 10) Why should wood applicator sticks not be used when carrying out a chemical reaction? Wood applicator sticks are made up of various chemicals that can be reactive with another compound, it can absorb some of the solution, and/or contaminate the solution.